The present invention relates to a process for making a silicone varnish resin system into a gel of suitable viscosity such that high density fillers can be suspended in the resin system without settling of the fillers during subsequent processing.
In the past, the art has employed diisocynates, such as methylene diphenyl diisocynate (MDI) which is illustrated below in a batch reactor environment for the gelling of silicone varnish resin systems. ##STR1##
The gelling occurs via an adduction reaction such as that illustrated below. ##STR2##
However, such an adduction reaction is subject to a number of disadvantages.
First of all, the reaction is not reproducible, i.e., there is a large variability in the amount of diisocynate which is required to obtain the desired degree of gellation. Furthermore, the reaction occurs slowly, e.g., the process can take as long as about 16 hours to occur at 150.degree. F.
The diisocynates employed are also sensitive to many contaminants, e.g., the lead present in the solder joints of paint cans. Moreover, the toxicity of the diisocynate compounds also renders them undesirable from a health and safety standpoint.
Accordingly, a need exists for an alternative method of gelling a silicone varnish resin.
Thus, it is an object of the present invention in order to provide such an alternative gellation process.
This and further objects will become apparent from the specification and claims that follow.